CSC 469H1 F ADVANCED OPERATING SYSTEMS 2006 Exam 2

CSC 469H1 F ADVANCED OPERATING SYSTEMS 2006 Exam 2 - CSC...

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../continued CSC 469H1 F ADVANCED OPERATING SYSTEMS UNIVERSITY OF TORONTO Fall 2006 Term Test #2 NO AIDS ALLOWED Please PRINT in answering the following requests for information: Family Name: _________________________________ Given Names: _________________________________ Student Number: |_ _ _| |_ _ _| |_ _ _| Login (@cdf): ____________________ Notes to students: 1. This test lasts for 110 minutes and consists of 89 marks. Budget your time accordingly. 2. This test has 8 questions and 11 pages (including this one); Check that you have all pages. 3. Write in pen. No pencils. Really, I mean it. 4. Write your answers on this “question and answer” paper, in the spaces provided. Be concise . In general, the amount of space provided is an upper bound on the “size” of answer that is expected. If necessary, use space where available and provide explicit pointers. 5. State your assumptions and show your intermediate work, where appropriate. 6. Do not go beyond here until instructed to do so. Write your student number at the top of each succeeding page once you get going. Question Marks 1 /15 2 /10 3 /16 4 /14 5 /10 6 /12 7 /6 8 /6 Total /89
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CSC 469H1F, Fall 2006, Term Test #2 Student Number: |_ _ _| |_ _ _| |_ _ _| ../continued 2 1. [15 marks, 3 each] Definitions Define the following terms, in the context of this course: a) Byzantine failure Failure model in which faulty process exhibits arbitrary behaviour. [Typically modelled as malicious attackers to capture worst case behaviour; faulty processes may collude with other failed processes but are not more powerful than non-failed ones.] b) Clustered page table Page table design in which (a) part of the virtual address is a hash key (as in hashed page tables) but (b) page table entries record mappings for a range of several consecutive pages. [Adv: provides fixed size page tables with low overhead (storage space and lookup time) for sparse and dense address spaces) c) Distributed Shared Memory Technique that allows distributed processes to transparently share a global virtual address space, although physical memory may be located on many nodes. [Typically builds on existing virtual address translation hardware, augmented with software support for remote page fetch and consistency control.] d) RAID Level 1 Mirrored disks. e) Vulnerability A software flaw with a security implication.
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CSC 469H1F, Fall 2006, Term Test #2 Student Number: |_ _ _| |_ _ _| |_ _ _| ../continued 3 2. [10 points] Superpages a) [2 points] Any paged virtual memory system requires both hardware and software support. What changes or additions to hardware are required to support superpages? The TLB entry format must include a page size field. b) [4 points] Describe 2 situations in which it may be desirable to demote a superpage. 1) On a write to a superpage, we don’t want to consider the entire superpage to be dirty, so we demote the superpage and mark only the base page that was actually written as being dirty. 2) Under memory pressure, we may want to demote a superpage so that we can detect if all the base pages in the superpage are actually still being used, allowing us to make better choices about what pages to evict.
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